Use of muscle activity indices as a relative measure of well-being in cultured sea bass Dicentrarchus labrax (Linnaeus, 1758)

Abstract

Aquaculture of sea bass is widely spread in the Mediterranean and employs a variety of husbandry protocols that need to be evaluated in terms of fish well-being. Behavioural tests can be used as operational indicators of short-term stress, because changes in swimming performance and/or muscle activity (e.g. electromyograms) can be interpreted as response associated with a wide variety of stressors. Diagnostic procedures, based on physiological telemetry, will thus enable appropriate mitigative strategies to be implemented to ensure the well-being of cultured fish. The objective of this study was to examine the contribution of two muscle types to the swimming activity of sea bass (Dicentrarchus labrax, L. 1758). Hard-wire technology was used to 'fine-tune' measures obtained using a physiological transmitter. Fine-tuning showed that the aerobic muscle displayed an increase in recruitment of muscle fibres relative to increasing swimming speed up to 0.6-0.7 ms -1 of the U crit , where the anaerobic (white muscle) activity started to exponentially augment with swimming speed, reaching up to~7 times its initial value. Intensity of electromyogram signals were described by logarithmic (red muscle): y = 0.5922Ln(x) + 1.2251 (R 2 = 0.9906) and exponential (white muscle): y = 0.0977e 2.4723x (R 2 = 0.9845) relationships. Fine-tuning indicated that the two muscle types in the sea bass are involved in fuelling swimming activity below the U crit . Thus, scope for activity is not supported solely using aerobic metabolism, though the red muscle powers the majority of the swimming ability. Measurement of U crit displayed an average value of 3.43 BLsec -1 (SE = 0.12). Associated EMG values measured during the forced swim trials using an implanted bio-sensitive radio transmitter showed that EMG's intensity increased, on average, 3.2 times between 0.2 msec -1 and the U crit velocity (~1 msec -1 ).Above EMG values were fine-tuned using estimates obtained from direct monitoring of the red and white musculature. Overall, the results demonstrated that the scope for activity, previously thought to represent only aerobic metabolism, is composed of both aerobic and anaerobic pathways. Fine-tuning of physiological transmitters to measure activity of free ranging fish can therefore Guest editors: be utilised to monitor the proportion of the scope of activity utilised in response to external stressors. This proportion and the level of compensatory ability remaining could represent a measure of well-being in cultured fish.

Modelling swimming activities and energetic costs in European sea bass (Dicentrarchus labraxL., 1758) during critical swimming tests

“…The data and analysis fill a knowledge gap on species-specific bio-energetic models for a wider range of species. As a consequence of the more accurate estimation of SFA and a better assessment of the energetic cost during swimming activity obtained in this study, it is also possible to calibrate the physiological tags more finely (Cooke et al 2000;Lembo et al 2007). …”

“…Parameters and statistics relative to the estimation of the models, respectively, of red and white muscle activity and oxygen consumption in the two experimental groups. Marine and Freshwater Behaviour and Physiology 3 and the red muscles following the procedures described in Lembo et al (2007). Fish were completely anaesthetized (stage 4: loss of reflex activity and no reaction to strong external stimuli, as reported by Iversen et al (2003) using 30 mg L −1 hydroalcoholic clove oil solution (eugenol)) (Massee et al 1995;Lembo et al 2007).…”

“…Marine and Freshwater Behaviour and Physiology 3 and the red muscles following the procedures described in Lembo et al (2007). Fish were completely anaesthetized (stage 4: loss of reflex activity and no reaction to strong external stimuli, as reported by Iversen et al (2003) using 30 mg L −1 hydroalcoholic clove oil solution (eugenol)) (Massee et al 1995;Lembo et al 2007). The time to reach stage 4 anaesthesia was about 5 min, and during the surgery, the gills were continuously irrigated with anaesthetic solution.…”

“…The fish were acclimatized at this low velocity for a minimum period of 20 min. The implanted fish were then subjected to critical swimming speed tests (U crit ) according to the protocol reported in Lembo et al (2007). They were tested at speed increments of 0.1 m s −1 every 15 min from a speed of 0.1 m s −1 until fatigued.…”

Behavioural indicators of welfare in farmed fish

“…Indeed, sustained swimming is characterised by low-frequency tail beats and a slow velocity (ca. one-third of maximum speed), while during prolonged swimming, fish can almost reach their maximum velocity (Lembo et al 2007). Several different tests have historically been used to quantitatively evaluate the swimming activity of fish (Beamish 1978).…”